The present invention relates to an improved method and apparatus for extracting the cement mantles used to secure prosthetic appliances, such as joint components, in bone recesses. In its more specific aspects, the invention is concerned with the removal of distally located cement plugs which are not readily removable by the invention of U.S. Pat. No. 4,919,153 by Albert K. Chin.
The invention of U.S. Pat. No. 4,919,153 achieves removal of an old cement mantle during revision arthroplasty by injecting new cement into the appliance cavity within the mantle left by removal of a prosthetic appliance, and then embedding a pulling tool within the cement. The new cement and old mantle bond into a unitary mass and then the pulling tool is used to remove the mass from the bone recess, as a unit.
In practice, it has been found that a solid plug of cement is often present distal to the tip of the cavity left by the removed prosthetic appliance. U.S. patent application Ser. No. 467,742, now U.S. Pat. No. 5,041,120 filed Jan. 19, 1990, a continuation-in-part of the application for U.S. Pat. No. 4,919,153, is concerned with a technique for removing this plug wherein the plug is drilled before the addition of new cement and the placement of the pulling tool. This allows the pulling tool to bond along most of the entire length of the cement mantle.
In many cases of cement extraction, it is impossible to pre-drill the plug, as provided by application U.S. Pat. No. 5,041,120 due to deviated alignment of the cavity within the mantle. Any attempt to drill such a plug will result in perforation of the femur. In these situations, the proximal portion of the cement mantle may be successfully extracted through the technique of U.S. Pat. No. 4,919,153, leaving a solid distal plug.
Prior art tap extraction systems for the removal of solid cement plugs employ a drill to first drill a bore into the plug and then a tap which, together with a slaphammer secured thereto, serves as a pulling tool to remove the plug. Unfortunately, these systems function poorly in the majority of cases. The solid plug is generally tightly held in the bone and available tap extractors strip out without removing the cement plug. In other cases, the tap extractor cracks the cement plug during extractor placement. Femoral perforation also occurs during drilling of the plug in preparation for tap placement. Strippage of the tap extractor occurs because the fluted configuration of the tap provides insufficient thread strength for plug removal. Plug drilling is difficult to perform without femoral perforation because of the long stem of the drill required to drill deep into the plug and the hardness and irregularity of the surface of the plug. The drill often glances off and punctures through the bone. After the plug is drilled, the tap is advanced through the drilled bore and often advanced too far, with resultant strippage of the cement threads. Radial forces exerted by the tap during tap placement also lead to cracking of the cement plug.